1. Field of the Invention
This invention relates to a lubricator for moving well equipment through a flow conductor.
2. The Prior Art
For various reasons, plugs or other well tools are positioned within well flow conductors prior to assembly of an underwater wellhead. Upon or after completion of the underwater wellhead, the plugs are removed to premit subsequent fluid flow through the conductor.
Some underwater wellheads are assembled within a submerged and enclosed work chamber. The work chamber is formed on the guide base of the underwater wellhead and provides a limited space within which personnel and equipment may maneuver. A portion of the underwater well flow conductor extends into the work chamber. Well equipment is run several feet through the flow conductor to retrieve the well plug therefrom.
Several factors prevent the use of conventional methods for retrieving such a well plug. First, the limited space inside the work chamber will not accommodate conventional wireline or pumpdown lubricators. Second, wireline equipment cannot develop the large downward forces required to unlock the well plug from the flow conductor. The distance between the well plug and the end of the flow conductor is too short for wireline equipment to develop those forces. Third, at this stage of the completion of the underwater well, the underwater wellhead is not fully equipped with pumpdown flow lines and related equipment. Conventional pumpdown operations therefore cannot be used to retrieve the well plug.
Rod-type lubricators have been used to run retrieval equipment. One form of rod-type lubricator has an elongate cylinder, a piston movable in the cylinder, and a single element rod. One stroke of the piston is designed to move the rod and the attached retrieval equipment a distance sufficient to reach the well plug. The rod extrudes longitudinally beyond the cylinder prior to the piston stroke. The stroke of the piston and the length of the rod are both greater than the distance between the end of the flow conductor and the well plug. The plugs are generally approximately 4 feet from the end of the flow conductor. The lubricator and extruded rod therefore have a longitudinal dimension in excess of 8 feet. Such a rod-type lubricator requires too much longitudinal space for some of the underwater pressure vessels presently utilized. When the reach rod extrudes, its end can engage the wall of the work chamber. If the piston should fail, the rod could be pushed through the chamber wall. The integrity of the chamber would be destroyed and the lives of the personnel therein endangered. Another form of rod-type lubricator employs a segmented rod. Otherwise, it is similar to the first form. Again, a single stroke of the piston moves the rod and the retrival equipment a distance sufficient to reach the well plug. During controlled movement of the piston, the rod segments may be added or removed as desired. However, failure of the piston could result in the rod being extruded. Under such circumstances, the entire length of the rod would extrude out of the lubricator. Due to space limitations in the work chamber, if that occurred, the end of the rod would engage and rupture the wall of the work chamber.